mpg question on older trailbazer

[ctrguy]

Hi guys, newbie here, stumbled across this place do to a vehicle concern,

I have an 02 trailblazer, with 140,000miles... this past summer i had new spark plugs installed, along with a fuel system flushing and filter change..
Recently i have seen my city mileage, which usually goes for 270 miles a tank drop to 200 miles per tank. (highway was about 300 and is now 270)

I checked my tires, and have no dummy lights going off...(plus recent plugs and fuel system checked...) Even tried a few additional fuel system cleaners, but to no avail. this is the inline six, not eight

Any suggestions, comments, or insight will be appreciated.

[maxwedge]

Welcome to AF, my 02 is about the same here in upstate NY, shorter trips, cold weather and the use of 10% eth. all contribute to this. Also you could do a full scan and look at all sensor inputs particularly o2 sensors.